1. Field of the Invention
The invention relates to a tire wheel structure and, more particularly, to a tire wheel structure equipped with a driving motor that is disposed near a tire wheel supported on a vehicle body and that drives the tire wheel by transferring driving force to the tire wheel.
2. Description of the Related Art
Japanese Patent Application Laid-Open Publication No. 6-48192 discloses a related-art tire wheel structure in which a driving motor for rotating a tire wheel is disposed within a wheel of the tire wheel. In this tire wheel structure, a drive shaft of the driving motor is connected to the wheel. Therefore, the tire wheel can be rotated by the torque generated by the driving motor.
In a construction in which the drive shaft of the driving motor is connected to the wheel and the tire wheel is rotated by the driving motor, the mass of the driving motor adds to the unsprung mass of the vehicle. In the aforementioned related-art tire wheel structure, the drive shaft of the driving motor is directly coupled to the wheel so that the driving motor and the tire wheel are integrally fixed to each other. In this structure, therefore, the driving motor is displaced together with the tire wheel as one unit with respect to the vehicle body, at the time of input of a road surface condition to the tire wheel. Thus, an adverse effect of the added unsprung mass becomes conspicuous. Specifically, the road following performance of the tire wheel during running of the vehicle deteriorates, and the passenger riding comfort degrades.